P3055 on 2018-2019 Buick Regal: DC/DC Converter Failure and Fixes

What's Unique About the 2018-2019 Buick REGAL

The sixth-generation Buick Regal, built on the GM E2XX platform, shares its start/stop architecture with many other GM vehicles from this era equipped with RPO KL9. The DC/DC converter's tendency to fail is so common that GM issued a widespread Technical Service Bulletin (TSB #21-NA-139) that explicitly covers the 2018-2019 Regal, along with models like the Chevrolet Malibu, Cadillac XT5, and Buick Enclave. This indicates a known issue with the component across numerous platforms, rather than a problem unique to the Regal itself.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp, MIL) is on
• Auto Start/Stop system is inoperative
• Message on the Driver Information Center (DIC) indicating a start/stop system issue
• Radio or infotainment screen reboots or cuts out during an auto-stop event.
• Vehicle may fail to restart after an auto-stop and require a jump start.
• Vehicle may be stuck in Park.
• Vehicle may not crank or start.

Most Likely Causes

1. Failed DC/DC Converter Module 🔴 High Probability This is a known failure point across many GM models using the start/stop system. TSB #21-NA-139 states the module can be misconfigured or fail internally, preventing it from boosting voltage correctly. It is the most common cause for P3055.
   How to confirm: Follow the diagnostic procedure in TSB #21-NA-139, which involves testing circuit 2172 for shorts to voltage or ground at terminal 10 of the T19 Power Supply Transformer connector. If no wiring faults are found ('infinite resistance'), the module is condemned.
   Typical fix: Replace the DC/DC Converter Module, also known as the Multi-Function Power Supply Converter. On platform mates, this part is located under the center console, accessible from the passenger footwell area. The replacement part does not require programming.
   Est. part cost: $110-$200
2. Poor Ground Connection 🟡 Medium Probability A related TSB for other GM vehicles (#18-NA-247) identifies poor ground connections (specifically G104, G107, G108) as a key cause due to issues like paint overspray or corrosion at chassis contact points. This can cause voltage irregularities that trigger the P3055 code.
   How to confirm: Visually inspect the main engine and chassis ground points for cleanliness and tightness. Perform a voltage drop test from the battery negative terminal to the chassis and engine block. TSB #18-NA-247 provides specific instructions for inspecting and cleaning these grounds.
   Typical fix: Clean the affected ground contact points of any paint or corrosion and tighten the fasteners to specification. GM provides detailed procedures for ground surface preparation.
   Est. part cost: $0
3. Weak or Failing 12V AGM Battery ⚪ Low Probability The DC/DC converter's operation is sensitive to input voltage. A weak battery can cause voltage instability that the system interprets as a converter fault. The complex charging systems on modern GM vehicles are highly dependent on battery state of health and charge.
   How to confirm: Have the battery professionally tested using a digital battery analyzer that can properly assess AGM batteries. A simple voltage check is often insufficient.
   Typical fix: Replace the 12V AGM (Absorbent Glass Mat) battery. Vehicles with start/stop systems require this specific type of battery. After replacement, the Battery Sensor Module may need to be reset using a scan tool.
   Est. part cost: $250-$350

Rare But Worth Checking

• Short or Open in Wiring Harness: TSB #21-NA-139 outlines a specific check for a short to voltage or ground on circuit 2172, which connects to the converter module. This can be caused by chafing against a bracket or another component. Another TSB, 21-NA-149, details common harness chafe points on related GM vehicles, emphasizing the need for careful visual inspection.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner to confirm P3055 is present.
2. Check for the presence of code P3056, as it often appears with P3055 and points to the same component.
3. Professionally test the 12V AGM battery. A weak battery must be ruled out first.
4. Inspect the main engine and chassis ground connections (G104, G107, G108) for corrosion and tightness, as outlined in TSB 18-NA-247.
5. If battery and grounds are good, follow the diagnostic procedure in TSB #21-NA-139.
6. Locate the T19 Power Supply Transformer (DC/DC Converter). On the Buick Regal and its platform mates, it is located in the center console area, accessible from the passenger footwell.
7. Disconnect the connector and test for a short to voltage on circuit 2172 at terminal 10 of the module's connector using a test lamp connected to a known good ground. The lamp should not light up.
8. If no short to voltage is found, test for a short to ground on the same circuit using a multimeter. The reading should be infinite resistance.
9. If no wiring faults are found (test shows infinite resistance), the TSB directs replacement of the T19 Power Supply Transformer (DC/DC Converter Module).

Parts You'll Likely Need

• DC/DC Converter Module (OEM #13510484) — This is the most common failure part for code P3055, as identified in GM's own service bulletin #21-NA-139.
  Trusted brands: ACDelco (Genuine GM)
  OEM price range: $110-$200
  Aftermarket price range: $90-$150

Related Codes That Often Appear With This One

• P3056 — This code is for 'DC/DC Converter Output Voltage 2 Performance.' Since P3055 and P3056 refer to the two different output channels of the same converter module, they frequently appear together when the module fails or has a wiring issue.
• C0800 — This code, for 'Control Module Power Circuit Low Voltage,' can appear in other modules like the Power Steering Control Module, indicating a systemic low voltage or ground issue that could also be the root cause of P3055.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-139: Malfunction Indicator Lamp (MIL) Illuminated - DTC P3055 Set. This is the primary bulletin for this issue and provides the full diagnostic tree, confirming the issue across many GM models including the Regal.
• 18-NA-247: While for the Equinox/Terrain, this TSB is relevant as it highlights poor ground connections (G104, G107, G108) as a cause for P3055 on similar GM platforms.

Platform-Specific Known Issues

• GM Technical Service Bulletin 21-NA-139 directly addresses DTC P3055 on the 2018-2019 Buick Regal, noting the cause may be a misconfigured or failed DC/DC converter module.
• Owners of platform-mate vehicles like the Chevy Malibu report that accessing the converter module can be difficult without removing the center console, though it is possible.

Mechanic-Grade Diagnostic Values

• Short to Voltage on Circuit 2172 — expected: A test lamp connected between terminal 10 of the T19 connector and a known good ground should NOT illuminate.. Failure: If the test lamp illuminates, it indicates a short to voltage on circuit 2172.
• Short to Ground on Circuit 2172 — expected: Infinite resistance (OL on most multimeters) between terminal 10 of the T19 connector and ground.. Failure: A resistance reading of less than infinite indicates a short to ground on the circuit.

Scan Tool Commands That Help

• GDS2 or equivalent: Battery Sensor Module Reset — This function should be used after replacing the 12V AGM battery to ensure the vehicle's charging system correctly adapts to the new battery's state of health.

Wiring & Ground Locations

• T19 Power Supply Transformer — Located in the center console area, typically accessed from the passenger footwell by removing trim panels.. This is the DC/DC converter module itself. Its connector is where diagnostic tests for wiring faults must be performed.
• T19 Connector, Terminal 10 — Pin 10 on the electrical connector for the DC/DC converter module.. This specific terminal carries the voltage for Circuit 2172 and is the precise point for testing for shorts to voltage or ground as per TSB #21-NA-139.
• G104, G107, G108 — These are chassis and engine ground points. While exact locations for the Regal were not found, TSB #18-NA-247 for the similar Equinox/Terrain platform indicates they are key ground connections to inspect. G103 on a related platform is on the left frame rail under the Starter Generator Control Module bracket.. Poor connections at these grounds due to paint or corrosion can cause system-wide voltage irregularities that trigger P3055, as noted in TSB #18-NA-247.

Real Owner Repair Stories

• YouTube video '2016 Chevy Malibu dtc P3055 P3056' (2016 Chevrolet Malibu (platform mate)) — Check Engine Light with codes P3055 and P3056. If the module is disconnected, the vehicle will not start or recognize the key.
  ❌ Tried (didn't work) Attempting to replace the module by only pulling back the side trim and carpet without removing the center console.
  ✅ What actually fixed it The problem was fixed by replacing the DC/DC converter module. The technician strongly recommended removing the entire center console (a ~15 minute job) for safe and proper access to the module and its very tight connectors, rather than trying to force it from the side.

OEM Part Supersession History

• 13462012, 13506066, 13509853, 13514044 → 13510484 — The supersessions likely address the internal misconfiguration or failure-prone components mentioned in TSB #21-NA-139. The newest part is engineered to meet rigorous factory standards for reliability.